1. Field of the Invention
The present invention relates to torque-coupling assemblies in general, and more particularly to a torque-coupling assembly provided with a venting passage.
2. Description of the Prior Art
Many modern vehicles employ all-wheel-drive (AWD) systems. Often, AWD systems do not require the operator to intentionally select this condition. These systems often employ a viscous clutch in the center differential to transfer torque to the drive wheels that are not sensed as slipping. In tight cornering situations and during towing, these AWD systems present a disadvantage. In cornering situations, noise and vibration can result from the AWD system being engaged. While this is not detrimental to the powertrain during short durations, it can be disconcerting to the operator.
Hydraulically actuated torque-coupling assemblies are used in various vehicular drivetrain applications to limit slip and transfer drive torque between a pair of rotary members. In all-wheel drive applications, hydraulically actuated torque-coupling assemblies are used to automatically control the drive torque transferred from a driven member to a non-driven member in response to speed differentiation therebetween. In limited slip applications, couplings are used in association with a differential to automatically limit slip and bias the torque distribution between a pair of rotary members.
Such hydraulic torque-coupling assemblies conventionally use a frictional clutch between the rotary members. The frictional clutch may be selectively actuated by various hydraulic actuator assemblies, which are constructed of elements disposed inside the differential casing. The hydraulic actuator assemblies internal to the differential case often include displacement pumps disposed inside the torque-coupling case and actuated in response to a relative rotation between the torque-coupling case and the output shaft. The displacement pumps are usually in the form of internal gear pumps, such as gerotor pumps adapted to convert rotational work to hydraulic work. In the internal gear pumps, an inner gear having outwardly directed teeth cooperates with an external gear having inwardly directed teeth so that fluid chambers therebetween increase and decrease in volume as the inner and outer gears rotate in a housing. By connecting the inlet and outlet of the device to the proper location along the sides of the gear set, the variable displacement chambers receive and discharge hydraulic fluid so that the device can function as a pump or motor. A shaft or other mechanical device can be connected to either the inner or outer gear depending upon the type of device. The hydraulic actuator assemblies further include a hydraulic piston member for frictionally loading the friction clutch.
While known hydraulic couplings, including but not limited to those discussed above, have proven to be acceptable for various vehicular driveline applications including the AWD systems, such devices are nevertheless susceptible to improvements that may enhance their performance and cost With this in mind, a need exists to develop improved hydraulic couplings and driveline apparatuses that advance the art.
For instance, there is a problem with the current hydraulic torque-coupling assemblies used in the AWD systems such that they do not have a simple on/off capability, which is separate and distinct from the hydraulic pressure supply/control circuit actuating the clutch assemblies.
The current hydraulically actuated torque-coupling assemblies used in the AWD vehicle systems are especially disadvantageous for a two wheel vehicle towing, such as, for instance, the towing with the two front wheels off the ground and tied to a tow truck and the rear two wheels rolling when the tow truck moves. When the motor vehicle equipped with the hydraulically actuated drive axle torque-coupling assembly in the rear axle is towed with two front wheels off the ground and rear two wheels rolling, the speed differential between a propeller shaft and rear axle shafts occurs. As a result of this, the hydraulic pump actuates the drive axle coupling assembly. The drive axle coupling assembly then drivingly couples the rear wheels to the front wheels. As a result, the motor vehicle could be dislocated from the tow truck.
Therefore, it is the intent of this invention to overcome the shortcomings of the prior art by providing an external control of the hydraulic pressure generated within a hydraulically actuated torque-coupling assembly in which the torque-coupling assembly can be selectively enabled or disabled, or set at any intermediate condition by controlling maximum system hydraulic pressure limit. It is the intent of this invention to overcome the shortcomings by providing an external control of the hydraulic pressure generated within a hydraulically actuated torque-coupling assembly in which the friction clutch can either be turned on or off, or set at any intermediate condition by controlling the maximum system hydraulic pressure limit.